It is standard to provide a motor vehicle with a lock system or an alarm that is operated remotely. A standard lock system which for example can control the vehicle's doors, the gas-tank cover, and the trunk or hatch, can be operated by a small transmitter carried on a key ring. The transmitter can either emit separate signals for locking and unlocking or can toggle the various latches between their locked and unlocked conditions with the same signal. Similarly the transmitter can also or alternatively turn the vehicle's security system on and off.
So long as the user is relatively close to the vehicle it is a relatively simple matter to see if it is locked or not by observing if the latch buttons are up or down, or if the alarm is on by observing a pilot light that is normally set to blink when the alarm is armed. In addition it is standard to provide another signal to indicate to the user from a greater distance what the condition of the latches or alarm is or even as described in German 44 22 906 to indicate that a door has not been fully shut. For instance the vehicle's lights can blink to indicate the condition, its horn can sound, or a separate alarm or beep can be emitted that allows a user even at some distance from the vehicle to ascertain if indeed the actuation of the transmitter has had the desired effect.
In other known systems such as described in U.S. Pat. No. 5,682,135 the user can carry an interactive device that automatically unlocks the vehicle and/or disarms the alarm system when near the vehicle, and that similarly automatically locks the vehicle and/or arms the alarm system when the user gets out of range. Such arrangements are normally also associated with some sort of warning system in the vehicle to indicate to the user, who is not very close to the vehicle, that indeed the desired effect has been achieved.
The most common system, whether the remote controller works by an IF, RF, or transponder basis, is for the vehicle to be provided with a separate beeping device that emits a characteristic signal--for instance one beep or a low note--when locking the vehicle or arming the alarm and another characteristic signal--for instance multiple beeps or a high note--when unlocking the vehicle or disarming the alarm. Thus even if the user is not looking at the vehicle, he or she has confirmation that the desired effect has been achieved.
The problem with such systems is that this acoustic signal is often annoying. Late at night when it is quiet or when the vehicle is inside it is frequently found to be excessively loud while during the day on the street it is barely perceptible. Thus there is a tradeoff between a loud signal that is certain to be heard and also likely to be found annoying, and a quieter one that might not be heard but is less likely to create unwanted noise pollution.